This application is based on Japanese Patent Application No. 2000-290149 filed Sep. 25, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a dynamic damper having a generally cylindrical shape, which is installed on a hollow or a solid rod member used as a vibration-transmitting member such as shafts, arms and conduits in various devices and being subject to oscillation or vibration, so that vibration of the rod member is reduced or absorbed.
2. Discussion of the Related Art
There are known various kinds of rod members such as shafts or arms functioning as a power-transmitting member and such as conduits or pipes serving as a fluid passage. Such a rod member generally tends to oscillate or vibrate and consequently suffers from problems of resonance thereof and undesirable transmission of the excited vibration therein to the other components of a device in which the rod member is used. As a method to cope with these problems, a dynamic damper is attached to the rod member. Examples of such a dynamic damper are disclosed in JP-A-2-190641, JP-B-6-37915 and JP-A-8-28627, wherein the dynamic damper has a metallic mass member having a generally cylindrical configuration and a pair of elastic support members formed on axially opposite sides of the mass member so as to extend axially outward directions, respectively. The disclosed dynamic damper is inserted onto the rod member and secured thereto at the elastic support members so that the mass member is elastically supported on the oscillating rod member via the elastic support members. Such a generally cylindrical dynamic damper is properly tuned so that the dynamic damper is capable of exhibiting effective damping characteristics with respect to a torsional or a circumferential vibration as well as a radial vibration of the rod member. Further, the mass member of the dynamic damper is less likely to drop off or released from the rod member, owing to its cylindrical shape, even if the elastic support member is undesirably broken. For these advantages, the dynamic damper has been used as a dynamic damper for a drive shaft of an automotive vehicle.
Such a conventional dynamic damper is installed onto the rod member such that the dynamic damper is disposed radially outwardly of the rod member. Therefore, the conventional dynamic damper is likely to interfere with other components disposed in the vicinity of the drive shaft, resulting in a limitation of the space for accommodating the dynamic damper. That is, the cylindrical dynamic damper is required to be made compact in its outside diameter.
Meanwhile, the cylindrical dynamic damper needs to have a sufficiently large mass of the metallic mass member, in order to effectively exhibit a desired vibration damping effect thereof. If the dynamic damper is made compact in size, however, the metallic mass member is accordingly made small in size, leading to difficulty in obtaining the desired mass of the metallic mass member. This results in deterioration of the vibration damping effect of the dynamic damper. Thus, the conventional dynamic damper has difficulty in meeting this downsizing requirement, sufficiently.
It is therefore an object of the present invention to provide a dynamic damper which is novel in construction and compact in overall size, while having a sufficiently large mass of a metallic mass member.
The above object may be attained according to the following modes of the invention each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the present invention is not limited to those modes of the invention and combinations of the technical features, but may otherwise be recognized based on the thought of the present invention that disclosed in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A dynamic damper mounted on a rod-shaped oscillating member, including: (a) a generally cylindrical metallic mass member formed of sintered metal or forging, and disposed radially outwardly of the oscillating member; (b) a pair of elastic support members which are formed on and extends axially outwardly and radially inwardly from axially opposite sides of the metallic mass member so as to have a tapered cylindrical configuration, the pair of elastic support members being adapted to elastically support the metallic mass member with respect to the rod-shaped oscillating member; and (c) an elastic covering layer integrally formed with the pair of elastic support members and being fixed in close contact with a substantially entire area of a surface of the metallic mass member for covering the substantially entire area of the surface of the metallic mass member, the metallic mass member having bevels in the form of tapered cylindrical surfaces, which are formed at radially inner edges of axially opposite end faces of the metallic mass member, respectively, each of the bevels extending over a corresponding one of the axially opposite end faces and an inner circumferential surface of the metallic mass member, to thereby chamfer the corresponding one of the radially inner edges, the pair of elastic support members are fixed at large diameter end portions thereof to the bevels, respectively.
In the dynamic damper constructed according to the above mode (1) of the present invention, the radially inner edges of the axially opposite end faces of the metallic mass member are chamfered to provide therein the bevels, and the pair of elastic support members are fixed at their large diameter end portions to the bevels, respectively. This arrangement permits that the large diameter end portions, i.e., the axially inner end portions of the elastic support members protrudes substantially axially inwardly from the opposite axial end faces of the metallic mass member, respectively, by a given axial distance which corresponds to the axial length of the bevels. This makes it possible to enlarge the axial length of the metallic mass member, thereby effectively assuring a sufficiently large mass of the metallic mass member, while permitting axially inward extension of the elastic support members from the respective axial end faces of the metallic mass member, thereby assuring a desired effective free length of the elastic support members. This arrangement also permits a decrease in the axial length of a part of each elastic support member which part protrudes axially outwardly from the corresponding axial end face of the metallic mass member, whereby the dynamic damper as a whole can be made compact in its axial length. Accordingly, the dynamic damper of this mode of the invention can meet compatibly both requirements for the sufficiently large mass of the metallic mass member and for the sufficiently reduced size of the overall dynamic damper, which are only alternatively achieved in the conventional dynamic damper.
In the dynamic damper according to this mode of the invention, the axially inner portions of the elastic support members, which are likely to suffer from the stress concentration upon application of the vibrational load to the damper, are secured to the bevels formed at radially inner edges of the axially opposite end faces of the metallic mass member, thereby effectively easing or relaxing the stress concentration generated in the axially inner portions of the elastic support members. Described in detail, the conventional dynamic damper including the cylindrical metallic mass member and the two elastic support members which are formed axially opposite sides of the metallic mass member for elastically supporting the metallic mass member, is likely to suffer from a stress concentration generated at or near a boundary between elastic support members and the axially opposite end faces of the metallic mass member. The presence of the radially inner edges of the axially opposite end faces of the metallic mass member, which edges have a generally right or sharp angle, may cause significant stress concentration at or near the boundary between elastic support members and the radially inner edges, possibly resulting in deterioration in durability of the elastic support members. However, the metallic mass member of the dynamic damper according to this mode of the invention is arranged to have the bevels formed at the radially inner edges of the axially opposite end faces thereof, respectively, for chamfering or eliminating the radially inner edges, and for dulling the angle of the radially inner edges. In the presence of the bevels, the metallic mass member has two corners having obtuse angles at radially inner portions of one of its axially opposite end faces, rather than the radially inner edge having the generally right angle. This arrangement makes it possible to ease the stress concentration generated in the axially inner edge portions of the elastic support members, thereby preventing occurrence of defects such as cracking in the elastic support members. Thus, the dynamic damper according to this mode of the invention can exhibit an excellent durability of the elastic support members.
According to this mode of the invention, the cylindrical metallic mass member is formed of sintered metal or forging. This arrangement permits a relatively high level of surface roughness of the metallic mass member of the dynamic damper of the present invention in comparison with a metallic mass member formed by casting or pressing. Accordingly, the elastic covering layer fixed in close contact with the rugged surface of the metallic mass member is firmly secured to the metallic mass member owing to a mechanical fixing force caused by engagement of raised and recessed portions between the rugged surface of the metallic mass member and the inner surface of the elastic covering layer which is rugged corresponding to the rugged surface of the metallic mass member upon vulcanization of a rubber material to form the elastic covering layer. Thus, the dynamic damper of this mode of the invention advantageously offers a desired fixing strength between the metallic mass member and the elastic covering layer, irrespective of whether the elastic covering layer is secured to the metallic mass member via an adhesive applied therebetween, thereby exhibiting desired vibration damping effect with sufficient stability.
Various kinds of known sintered metallic materials including pure iron type, iron-carbon type, and iron-copper type may be employed for the metallic mass member of the dynamic damper according to the present mode of the invention, taking into account the required mass of the metallic mass member, the manufacturing cost, working conditions of the dynamic damper and the like. Further, various kinds of known forging or forged members, such as a carbon steel may be used as the metallic mass member, and the metallic mass member may be formed by hot forging or alternatively by cold forging. The employed forging should be subjected to a scale removal treatment by a shot blasting method or the like. In this respect, the process for removing the scale of the forging is generally performed upon manufacturing the forging. Therefore, the present invention requires no specific facilities or manufacturing process for performing the scale removal treatment on the metallic mass member, and accordingly no increase in the manufacturing cost.
Various kinds of rubber materials may be employed for forming the elastic support member and the elastic covering layer which are integrally formed with each other, depending upon required vibration damping characteristics of the dynamic damper of the present mode of the invention. For instance, a rubber material such as NR (natural rubber), SBR (styrene-butadiene rubber) or BR (butadiene rubber), or a mixture of any two or more thereof may be suitably used. The elastic covering layer is only required to cover the substantially entire area of the surface of the cylindrical metallic mass member, and is not necessarily required to cover local portions of the metallic mass member to which supporting members of the mold are butted, for supporting and positioning the metallic mass member in the mold.
(2) A dynamic damper according to the above-indicated mode (1), wherein the elastic support members have respective inner circumferential surfaces whose large-diameter end portions located axially inwardly from the axially opposite end faces of the metallic mass member.
In the above-indicated mode (2), the presence of the bevels of the metallic mass member permits the elastic support members extend radially inwardly from the respective axial end faces of the metallic mass member, so that the dynamic damper can be made smaller in its axial length, effectively. In this respect, the large diameter end portion of the inner circumferential surface of each elastic support member should be generally interpreted as a point of intersection of an axial continuation of the radially inner circumferential surface of the elastic covering layer which extends parallel to the center axis of the dynamic damper, and an axial continuation of the inner circumferential surface of the elastic support member which inclined at a predetermined tapered angle of the elastic support member to the center axis of the dynamic damper.
(3) A dynamic damper according to the above-indicated modes (1) or (2), wherein each of the elastic support members is fixed to the corresponding one of the bevels of the metallic mass member such that a centerline of the elastic support member which extends through a center portion of the elastic support member in a width direction of the elastic support member, is intersect with the corresponding bevel of the metallic mass member.
In the above mode (3), the centerline of the elastic support member in its width direction can extend axially outwardly from the corresponding bevel of the metallic mass member. In this arrangement, the dynamic damper further advantageously offers effects of the bevels, resulting in elongated free length of the elastic support members and decrease in the axial length of the dynamic damper owing to the axially inward extension of the elastic support members.
(4) A dynamic damper according to any one of the above-indicated modes (1)-(3), wherein the elastic support members have respective outer circumferential surfaces whose large-diameter end portions located on the respective bevels of the metallic mass member, as seen in an axial projection of the dynamic damper.
In this mode (4), the elastic support members are arranged such that the substantially overall elastic support members extend axially outwardly from the bevels of the metallic mass member, respectively. In this arrangement, the dynamic damper yet further advantageously offers the effects of the bevels of the metallic mass member, resulting in the elongated free length of the elastic support members, and the decrease in the axial length of the dynamic damper due to the axially inward extension of the elastic support members.
(5) A dynamic damper according to any one of the above-indicated modes (1)-(4), wherein the elastic covering layer is fixed in close contact with a surface of the metallic mass member without using an adhesive.
In this mode (5), the metallic mass member needs not to be subjected to an adhesive treatment, e.g., an application of an adhesive to the surface of the metallic mass member. This elimination of the adhesive treatment leads to reduction in cost of manufacture and improved production efficiency of the dynamic damper. Even if the elastic covering layer is fixed to the metallic mass member without using the adhesive, the elastic support members integrally formed with the elastic covering layer can be firmly secured to the metallic mass member, since the metallic mass member is formed of sintered metal or forging and the elastic covering layer is fixed in close contact with and covers the substantially entire area of the metallic mass member. In order to form and closely secure the elastic covering layer on and to the surface of the metallic mass member, it is desirable to integrally form the elastic covering layer and the elastic support members by vulcanizing a rubber material to form the elastic covering layer and the elastic support member in a mold wherein the metallic mass member is placed in position relative to the mold. In this respect, the metallic mass member needs not be subjected to the adhesive treatment, but may be subjected to other treatments such as washing and degreasing, as needed.
The thickness of the elastic covering layer is preferably not less than 0.5 mm, more preferably not less than 1.0 mm, in order to obtain sufficient fixing strength thereof to the cylindrical metallic mass member and sufficient durability thereof. Further, the thickness of the elastic covering layer is also preferably not more than 5.0 mm, more preferably not more than 3.0 mm, in the light of the fact that the excessively large thickness of the elastic covering layer may lead to an undesirable increase in the size of the dynamic damper and an undesirable restraint on the diametrical dimension of the metallic mass member.
(6) A dynamic damper according to any one of the above-indicated modes (1)-(5), wherein the metallic mass member includes a plurality of through holes formed therethrough so as to extend in an axial direction of the metallic mass member, the plurality of through holes being filled with the elastic covering layer.
In this mode (6), with the through holes being filled with the elastic covering layer, the radially outer and inner parts of the elastic covering layer which cover the respective outer and inner circumferential surfaces of the metallic mass member are integrally connected via the elastic covering layer filling the through holes. In this arrangement, the metallic mass member exhibits resistance force with respect to the displacement in its axial and radial direction relative to the elastic covering layer, so that the elastic covering layer can be fixed to the metallic mass member with improved fixing strength. Thus, the dynamic damper of this mode can exhibits a desired vibration damping effect with improved stability. Preferably, the dynamic damper according to this mode of the invention may be incorporated with the aforementioned mode (5), so as to effectively increase the fixing strength between the metallic mass member and the elastic support members that are bonded with each other without using the adhesive.
In the dynamic damper according to the present invention, the bevels can be formed at the same time when the metallic mass member is formed by sintering the compressed metallic power or by forging. In this mode (6), the dynamic damper is preferably formed of the sintered metal so that the plurality of through holes can be formed at the same time when the metallic mass member is formed by sintering the metallic powder pressed into a desired mold for forming the metallic mass member of the dynamic damper according to this mode (6). In order to form concurrently the bevels and the plurality of through holes with ease, upon forming the metallic mass member, it is preferable to use a mold consisting of a plurality of components which are butted together at a parting plane or planes extending in the direction perpendicular to the longitudinal direction of the mold, to thereby define therebetween the mold cavity.
(7) A dynamic damper according to any one of the above-indicated modes (1)-(6), wherein the surface of the metallic mass member has a ten-point mean roughness Rz within a range from 30 xcexcm to 200 xcexcm.
Namely, an excessively small Rz value of the surface roughness of the metallic mass member leads to difficulty in obtaining a sufficient fixing stability between the metallic mass member and the elastic covering layer, while an excessively large Rz value of the surface roughness of the metallic mass member may lead to deterioration of efficiency and increased cost of manufacture. In the above mode (7), the metallic mass member is arranged to have a ten-point mean roughness Rz within a range from 30 xcexcm to 200 xcexcm, thereby effectively offering the metallic mass member which assures sufficient bonding stability between the metallic mass member and the elastic support members. Preferably, the metallic mass member is arranged to have a ten-point mean roughness Rz within a range from 50 xcexcm to 100 xcexcm, resulting in further improved fixing stability between the metallic mass member and the elastic covering layer.
(8) A dynamic damper according to any one of the above-indicated modes (1)-(7), wherein the bevels are dimensioned such that the radially inner edges of the axially opposite end faces of the metallic mass member are chamfered by 3.0-5.0 mm in an axial direction and a radial direction perpendicular to the axial direction of the metallic mass member, respectively.
If the bevels are excessively small in size, the bevels surfaces are less likely to permit the axially inwardly extension of the elastic support members and to ease the stress concentration generated in the boundaries between the elastic support members and the bevels of the metallic mass member. On the other hand, if the bevels are excessively large in size, it becomes difficult to assure a required mass of the metallic mass member sufficiently. In this mode (8), the radially inner edges of the axially opposite end faces of the metallic mass member are chamfered by 3.0-5.0 mm both in the axial and radial directions of the metallic mass member, so that the dynamic damper can have a sufficiently large mass of its metallic mass member, while permitting the axially inward extension of the elastic support member so that the axial length of the dynamic damper is made small.